The present invention relates to an position sensor, and more particularly to a sensor used in the automotive industry to detect the position of various mechanical or control components, such as steering column, light switches, windshield wiper switches, etc.
There exists a need to know the position of mobile levers, such as those used to control a vehicle or to monitor its levels, for example, fuel or other motor fluids. The increased number of electronic components used in modem vehicles also increases the need to access a greater number of mechanical operating parameters, such as the position of levers or activating devices, the torque applied to the drag link, the position of the shift lever, etc.
Current technology makes use of resistive potentiometers. In order to increase reliability, it would be preferable to replace this type of sensor by no-contact sensors, without, however, increasing their cost. One such sensor relates to a device that includes a measuring coil encased between two, opposite polarity field coils installed on a cylinder (or flat plate) which has a V-shaped internal plate made of ferromagnetic material, and in which slides a small magnet. Inside this core, the magnet generates a saturation area that interrupts the lines of the field created by the field coils, thereby modifying each one of them in the signal measured at the terminals of the measuring coil. The magnet is then attached to the moving part whose travel one wishes to measure. In the case of the flat form of the device, the small magnet moves upon contact with a protective and frictionless layer between two coils, and here also, the measurement is obtained differentially. This type of device is not suitable for remote or cross-panel position measurements. Furthermore, construction of the cylindrical version of the device is relatively complex, whereas the flat version produces unwanted friction.
The purpose of the present invention is to eliminate the aforementioned inconveniences by providing a no-contact analogue position sensor that can be manufactured economically, easily installed and has the ability to measure a position through a separation.
The present invention involves the use of a coil to create inductance, the coil being positioned on a thin substrate sandwiched between two (or at least one) layers of mumetal-type (high magnetic permeability) material. In the following description, the term xe2x80x9cMumetalxe2x80x9d shall be generically used to designate any materials having analogue magnetic properties (i.e., high magnetic permeability; for example, 100,000 times that of air, and low saturation field; for example, 0.8 Tesla)
The mumetal acts as an amplifier for the inductance L measured at the terminals of the coil (magnetic field storage effect). When a magnet passes in front a sheet of mumetal, its magnetic field locally saturates the mumetal (the composition of which is selected to allow saturation by a relatively weak field), whose magnetic permeability collapses on the saturated surface.
The result is a reduction of the inductance factor (L) in proportion with that area of the coil covered by the saturated mumetal. This reduction in inductance is measured at inductance terminals, thereby giving an estimation of that area of the coil that has been covered by the saturated mumetal.
Two parallel coils, positioned between each layer of mumetal, can also be used; one being powered by alternating current, and the other connected to the terminals of a voltage measuring device. In this case, the mumetal promotes the coupling between the two coils. The saturation of the mumetal by the magnetic field of the magnet produces a coupling variation proportionate to the area of the coil that has been covered with saturated mumetal, which can be measured at the terminals of the second coil.
By determining the appropriate design and layout of the coil, mumetal and magnet, one can obtain an electrical signal (inductance or coupling variations) corresponding to the movement of the magnet in a predetermined direction.